The sporulation and germination-outgrowth developmental cycle of Bacillus subtilis provides a model biological system for examining intracellular differentiation. In view of the increasing evidence implicating the aminoacyl-tRNA synthetases and tRNA in developmental processes, it is suggested that a study of their possible regulatory functions in this defined system should prove to be of major import. Specific areas of study will include: (1) An examination of the roles of lysyl- and tryptophanyl-tRNA synthetases in regulating amino acid biosynthesis and protein turnover during spore outgrowth, vegetative growth and sporulation; (2) An examination of the effects of tRNA maturation mutants on the events in sporulation and spore outgrowth. BIBLIOGRAPHIC REFERENCES: W. Steinberg. 1975. Sporulation of Bacillus subtilis cells = In vivo evidence for phenotypic modification of a thermosensitive lysyl-transfer ribonucleic acid synthetase, p. 290-300. In P. Gerhardt, R. N. Costilow and H. L. Sadoff (ed), Spores VI. American Soc. Microbiol., Washington, D.C.